Distributors of the type indicated are used particularly but not exclusively in the technical field of sowing machines with pneumatic seed transportation. In these applications, it is known to provide a seed-loading hopper to which a dosing device, for example, of the volumetric type, is fitted; the dosing device supplies metered quantities of seed into a Venturi duct (in short a “Venturi”) by means of which the seed is introduced into an air-flow in a main duct of the distributor. The air-flow is generated by forced ventilation, for example, by means of a blower or similar air-pressurization means so as to convey the air and seed mixture towards the sowing regions in a jet.
The limitations imposed by the overall size of the distributor, which is dictated partly by the size of the components used as well as by the space offered by the machine equipped with the distributor, generally suggest the use of a Venturi having a narrow cross-section with a diameter no greater than preset values. However, these dimensional limitations of the Venturi duct penalize the utilization of the power deliverable by the blower that is used to produce the forced ventilation in the air flow; this power is thus only partially transferred to the air and seed mixture in the respective static and kinetic energy components, resulting in low efficiency and low flow-rates of material delivered in comparison with those that could theoretically be achieved with the power used.